1. Field of the Invention
The present invention relates to an electric power steering controller provided with a function for detecting the failure of a motor driving direction discrimination means of the electric power steering controller using a motor as its power source.
2. Description of the Prior Art
Such an electric power steering controller has been disclosed in, for example, U.S. Pat. No. 4,896,735. The controller logically compares right-and left-direction driving signals output by a computer in accordance with an output signal of a torque detector with right- and left-direction driving signals output by a motor driving direction discrimination means in accordance with an output signal of the torque detector by an AND circuit. Then, the motor driving direction is determined to be the direction of direction driving signals that match among these driving signals. As a result, it is possible to prevent the steering wheel from rotating due to a failure or runaway of the computer.
In this existing electric power steering controller, the rotational direction driving signal input from a torque detector and judged by a computer is compared with a direction driving signal output from a motor driving direction discrimination means by an AND circuit and the motor driving direction discrimination means enables driving of a motor when both signals coincide with each other. As a result, even if a failure occurs where the computer drives the motor independently of steering torque, it is possible to ensure safety because the motor driving direction is controlled by the motor driving direction discrimination means. However, where there is a failure in the motor driving direction discrimination means so as to enable driving of the motor, it is impossible to ensure safety because the computer cannot detect the failure of the motor driving direction discrimination means. That is, a backup system is not constituted for safety.